Software will be developed that will allow scientists to quickly and easily solve a wide array of ordinary and partial differential equations on microcomputers capable of running MS-DOS, the Apple Macintosh and UNIX operating systems. This software will provide users with easy access to capabilities far beyond those available from other microcomputer differential equation solvers. These include the choice of a variety of computational techniques for ODEs (stiff and non-stiff solvers) and the solution of PDEs by the method of lines, by moving finite element methods and by various adaptive methods. These methods will allow the solution of a wide class of problems that arise in biological, physical and chemical systems. The software will be capable of parameter estimation for both ODEs and PDEs, and will be capable of handling delay equations and difference equations. In the later part of the Phase II work, the software will be incorporated into the MicroMath Scientific Computing Environment, a modular system for general scientific problem solving currently being proposed. The Phase II DIFFEQ software is intended to be a powerful and easy-to-use model development tool for scientists, engineers, undergraduates and graduate students in the health sciences.